As examples of a refrigerant evaporator, a multi-flow type heat exchanger and a serpentine flow-type heat exchanger are known in U.S. Pat. No. 6,339,937 (Unexamined Japanese Patent Publication No. JP-A-2001-324290) and Un examined Japanese Patent Publication JP-A-2001-12821. In the multi-flow type heat exchanger, a core portion having a plurality of tubes is arranged between an upper and lower tanks. It is constructed such that a refrigerant flows in the plural tubes at the same time. In the serpentine flow-type heat exchanger, the refrigerant flows in a similar manner.
In the core portion, the tubes are arranged in a direction perpendicular to a flow direction A of air passing outside of the heat exchanger. Hereafter, a direction in which the tubes are arranged is referred to as a core width direction D1 or a right and left direction of the heat exchanger. A downstream side of the core portion with respect to the sir flow direction A is referred to as a front side and an upstream side of the core portion with respect to the air flow direction A is referred to as a rear side.
For example, in a refrigerant evaporator shown in FIG. 19, a plurality of flat tubes 120 are layered between an upper tank 116 and a lower tank 118. The tubes 120 forms a core portion 122. A refrigerant inlet connector 112 and are frigerant outlet connector 114 are connected to a left end and a right end of the upper tank 116. A separator 124 is provided in a middle portion of the upper tank 116. The refrigerant flows in the left tubes 120, which are arranged in a left section of the core portion 122, at the substantially same time and makes a turn in the lower tank 118 from the left side to the right side. Then, the refrigerant flows in the right tubes 120, which are arranged in a right section of the core portion 122. Thus, a refrigerant first pass P1 is made in the left section and a refrigerant second pass P2 is made in the right section, when viewed in a broad aspect. Here, even if the refrigerant evaporator is placed such that the upper tank 116 and the lower tank 118 extend vertically and the tubes 120 are layered in a vertical direction, the direction that the tubes 120 are layered is still referred to as the core width direction D1.
In the above left-right U-turn type evaporator, if the refrigerant has super heat, temperature distribution is likely to be generated in the right section of the core portion 122 in which the second refrigerant pass P2 is made. As a result, temperature of air blown from the left section and the right section will be uneven.
Also in a case that the refrigerant does not have super heat, it is necessary to uniformly distribute the liquid refrigerant in the right tubes 120 because the amount of the refrigerant is generally small. If the refrigerant is not uniformly distributed in the tubes 120, the refrigerant will be dried out, that is, completely evaporated in the tubes 120 in which the amount of the refrigerant is small. As a result, the temperature of air is not uniform.
To solve this problem, a 2-2 pass-type evaporator shown in FIGS. 20A, 20B is proposed. It is for example disclosed in U.S. Pat. No. 6,272,881B1 (JP-A-11-287587). In the 2-2 pass-type evaporator, a front core portion 122A and a rear core portion 122B are arranged between a pair of upper tanks 116A, 116B and a pair of lower tanks 118A, 118B. A refrigerant inlet and outlet connector 113 is connected to a upper left end of the upper tanks 116A, 116B. A separator 124A is provided in the upper front tank 116A, which communicates with the refrigerant inlet and a separator 124B is provided in the upper rear tank 116B, which communicates with the refrigerant outlet. Thus, two refrigerant passes P1 and P2 are made in the front core portion 122A and two refrigerant passes P3 and P4 are made in the rear core portion 122B, from a broad view. As shown in FIG. 20B, the front core portion 122A is constructed of a row of tubes 120A and the rear core portion 122B is constructed of a row of tubes 120B. Corrugated fins 126 are interposed between the tubes 120A, 120B.
In the above evaporator, since the refrigerant flows through four passes P1 to P4, the flow distance of the refrigerant is long. Also, the refrigerant turns many times. That is, the numbers that the refrigerant flows in and out the tubes 120A, 120B and the core portions 122A, 122B is increased (four times in FIG. 20A). Therefore, the pressure loss of the refrigerant is increased throughout the evaporator. As a result, the performance of the evaporator is deteriorated.
To solve this problem, a front and rear U-turn type evaporator is proposed, as shown in FIG. 21. In the evaporator, separators are not provided in the tanks 116A, 116B. Thus, the refrigerant flows in all front tubes 120 in the front core portion 122A and makes turn from the front side to the rear side in the lower tanks 118A, 118B. Then, the refrigerant flows in the rear tubes 120 of the rear core portion 122B. This kind of evaporator is for example disclosed in Unexamined Japanese Publication No. JP-A-2003-75024 (WO02103263). In this evaporator, the pressure loss is likely to be reduced and the temperature difference of air is likely to be reduced.
Recently, in the vehicle air conditioning apparatus, it is required to independently control the temperature of air between a right region and a left region of a passenger compartment. Therefore, it is difficult to adapt the above evaporator to such vehicle air conditioning apparatus.
In the above evaporator, in a core section through which a large amount of air flows, heat exchange is performed between air and the refrigerant and the air is cooled. Because an amount of the refrigerant evaporation is large, the pressure loss is increased with an increase in the air volume. On the other hand, in a core section in which an air flow amount is small, the amount of the refrigerant evaporation is small. Therefore, the increase in the air volume is small and the pressure loss is not increased greatly. As a result, in the full pass-type evaporator shown in FIG. 21, the refrigerant easily flows in the core section where the volume of air passing therethrough is small, that is, the core section where the pressure loss of the refrigerant is small. Therefore, it is difficult to maintain cooling performance at the core section where high cooling performance is more required, that is, the core section where the air volume is large. Also, in the large air section, the refrigerant easily has the super heat and is dried out. Therefore, it is difficult to uniform the temperature of air.